For the construction materials and window materials for vehicles, such as automobiles, trains, ships and airplanes, the window materials for housing and the glass plates used in showcases, in addition to transparency, electrical conductivity for preventing electrostatic charges and infrared cut-off characteristics are required in some cases. As materials for such applications, indium tin oxide powders and antimony-doped tin oxide powders have been known. Here, although indium tin oxide powders exhibit excellent transparency and infrared cutting performance and are thus advantageous, it incurs a high cost because they are expensive. On the other hand, although antimony-doped tin oxide powders are inexpensive as compared with indium tin oxide powders, there are problems not only of low visible light transmittance which makes it impossible to cope with the demand for high transparency, but also of the infrared cutting performance being inferior to that of indium tin oxide powders.
On the other hand, although there are applications as long as the infrared cut-off characteristics are favorable even if the visible light transmittance is about 70%, the currently available antimony-doped tin oxide powders do not necessarily exhibit satisfactory infrared cut-off characteristics.
Although the inventors of the present invention considered that an increase in the amount of antimony added was necessary in order to improve the infrared cut-off characteristics of antimony-doped tin oxide powders, if the amount of antimony addition was increased by a known method (see Patent Document 1), there were problems in that a portion of antimony was not incorporated into the crystal lattice of tin oxide and was not doped, and that the crystallinity of antimony-doped tin oxide was reduced, which lowered the electrical conductivity.